A disk apparatus such as a hard disk apparatus may have an inaccurate head positioning signal attributable to mechanical resonance of the head positioning mechanism or the like. In a system where the head positioning process is controlled in discrete time, when a disturbance component of a frequency equal to or greater than a Nyquist frequency is applied, a sampled head positioning signal may cause an aliasing component to appear. Depending on the type of frequency region where the aliasing component appears, the aliasing component may cause adverse effect on the head positioning control.